The purpose of this investigation is to define the mechanism by which vitamin B-12 is incorporated by mammalian cells. In vitro experiments will be performed with isolated rat ileal and hepatic cells, murine leukemia cells, and hamster embryo cells both before and after neoplastic transformation. Utilizing purified B-12 transport proteins, we plan to look at B-12 incorporation and processing by whole cells and isolated subcellular compounds. We wish to examine similarities and/or differences in uptake mediated by intrinsic factor, transcobalamin II and R-binders of B-12 in normal and neoplastic cells to further our understanding of B-12 transport and possibly to help define the role of B-12 in mammalian cellular metabolic functions.